A light shield that allowed only a spot of light about the size of an egg to shine out. Typically, such a shield was a metal chimney for a coal oil light. About halfway up the chimney there was a hole approximately the size of an egg. By holding an egg in front of the hole (light source), it was possible to detect such things as embryos.
1001 Words and Phrases You Never Knew You Didn’t Know by W.R. Runyan Copyright © 2011 by W.R. Runyan